Method for the preparation of a fibrous lithium-ion battery based on a cross-scale electrode skeleton

Abstract

This invention provides a method for fabricating a fibrous lithium-ion battery based on a multi-scale electrode framework, comprising the following steps: 1) growing carbon nanotubes on the surface of a fibrous conductive material using chemical vapor deposition to serve as a multi-scale electrode framework; 2) in-situ loading LiFePO4 onto the multi-scale electrode framework using a hydrothermal reaction to serve as a composite cathode; 3) in-situ loading Li4Ti5O onto the multi-scale electrode framework using a hydrothermal reaction. 12 4) A separator is wrapped around both the composite positive and composite negative electrodes, which are then placed in heat-shrink tubing, filled with electrolyte, and sealed to obtain the fibrous lithium-ion battery. The assembled fibrous lithium-ion battery achieves a linear capacity density of 1.1 mAh / cm² and a linear energy density of 2.74 mWh / cm². It retains 98% of its discharge specific capacity under 180° bending conditions, exhibiting excellent deformation stability and broad application prospects in the field of wearable electronics.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of fibrous batteries, and particularly relates to a preparation method of a fibrous lithium ion battery based on a cross-scale electrode framework. BACKGROUND

[0002] In recent years, with the development of various electronic products towards portability, wearability, flexibility and the like, flexible lithium ion batteries have attracted more and more attention, and in particular, fibrous lithium ion batteries have become a research hotspot in the field of flexible energy storage due to their excellent bending flexibility, deformation adaptability and weavability. At present, the fibrous lithium ion battery usually adopts a linear or fibrous current collector (such as aluminum wire, copper wire, carbon fiber, carbon nanotube fiber, graphene fiber, metal composite yarn and the like) to load active material as a composite positive electrode or a composite negative electrode. However, due to the limited specific surface area of the commonly used linear or fibrous current collector, the amount of active material that can be loaded is small, resulting in low capacity and energy density of the fibrous battery, which cannot meet the long endurance requirements of the current wearable and portable batteries. If the loading amount of active material on the existing linear or fibrous current collector is increased, the internal resistance of the electrode will also be increased, which will affect the rate performance of the lithium ion battery and cannot meet the requirements of the current battery fast charging and discharging.

[0003] In the field of traditional lithium ion batteries, in order to increase the specific surface area of the active material loaded on the current collector, a method of growing carbon nanotubes in situ on the current collector can be used to improve the capacity and energy density of the lithium ion battery. For example, Abdollahi et al. grew arrayed carbon nanotubes on a stainless steel sheet current collector and further loaded manganese dioxide active material to assemble a button lithium ion battery. Due to the introduction of the arrayed carbon nanotubes, the capacity and energy density of the battery were significantly improved (Electrochimica Acta 2021, 390, 138826). However, there is currently no literature report or public patent on growing carbon nanotubes on the linear or fibrous current collector in the fibrous lithium ion battery to increase the loading amount of active material. In addition, since the fibrous lithium ion battery needs to be able to withstand bending, folding and other deformations, after growing carbon nanotubes and loading active material on the linear or fibrous current collector, the microstructure and morphology of the fibrous lithium ion battery need to be maintained without being destroyed under various deformations in order to stabilize the energy storage performance of the fibrous lithium ion battery. SUMMARY

[0004] The present application is directed to the problems existing in the prior art, and provides a preparation method of a fibrous lithium ion battery based on a cross-scale electrode framework.

[0005] The object of the present application can be achieved by the following technical solutions:

[0006] The preparation method of the fibrous lithium ion battery based on the cross-scale electrode skeleton of the application comprises the following steps:

[0007] 1) growing carbon nanotubes on the surface of the fibrous conductive material as the cross-scale electrode skeleton by using a chemical vapor deposition process;

[0008] 2) loading LiFePO4 on the cross-scale electrode skeleton in situ as a composite positive electrode by using a hydrothermal reaction;

[0009] 3) loading Li4Ti5O 12 on the cross-scale electrode skeleton in situ as a composite negative electrode by using a hydrothermal reaction;

[0010] 4) wrapping the composite positive electrode and the composite negative electrode with a separator respectively, loading them into a heat shrinkable tube, filling electrolyte, and packaging to obtain the fibrous lithium ion battery.

[0011] Wherein, the sequence of step 2) and step 3) is not limited.

[0012] Further, in step 1), the fibrous conductive material is selected from any one of carbon fiber, carbon nanotube fiber, graphene fiber, nickel wire and stainless steel wire.

[0013] Further, in step 1), the diameter of the fibrous conductive material is 1-500 μm.

[0014] In the application, the meaning of the "cross-scale electrode skeleton" is that the conductive material with nano, micro or millimeter structure scale is used as the conductive skeleton to load LiFePO4 and Li4Ti5O 12 and other active substances. The meaning of the "fibrous conductive material" is that the fibrous material with the resistivity less than 1×10 -3 Ω / cm and the aspect ratio greater than 1000.

[0015] Further, in step 1), the chemical vapor deposition process is as follows: the surface of the fibrous conductive material is cleaned with deionized water and ethanol, and after drying, the fibrous conductive material is placed in a high-temperature tube furnace, argon is introduced, and then heated to 850℃, followed by injecting a carbon source solution containing a catalyst into the tube furnace to grow carbon nanotubes, the injection speed is 2-20 mL / h, and the growth time is 5-30 min. More preferably, the injection speed is 2 mL / h, and the growth time is 10 min.

[0016] Further, in the step 1), the carbon source solution containing the catalyst is a mixed solution of ethanol, dimethylbenzene, ethylenediamine and ferrocene, wherein the ferrocene is used as the catalyst, the volume ratio of ethanol, dimethylbenzene and ethylenediamine is 1:1:0.1-0.2, and the concentration of ferrocene is 0.1-0.2 mol / L.

[0017] The present application can realize the regulation of the orientation structure, growth length and growth density of carbon nanotubes by regulating the concentration of the catalyst, the ratio of the carbon source, the injection speed, the growth time and other process parameters, and can obtain an array orientation structure or a random orientation structure, the growth length can be regulated in the range of 5-100 μm, and the growth density can be regulated in the range of 0.1-0.5 mg / cm 2 The growth density of the carbon nanotubes is obtained by calculating the mass of the carbon nanotubes grown on the fibrous conductive material per unit area.

[0018] Further, in the step 2), the LiFePO4 is in-situ loaded on the cross-scale electrode skeleton by using a hydrothermal reaction, and the process is as follows: a mixed aqueous solution A of lithium hydroxide, ferrous sulfate and ethylenediaminetetramethylene phosphonic acid is prepared, the concentration of lithium hydroxide is 6-36 mol / L, the concentration of ferrous sulfate is 2-12 mol / L, and the concentration of ethylenediaminetetramethylene phosphonic acid is 0.5-3 mol / L; the cross-scale electrode skeleton obtained in the step (1) is immersed in the mixed aqueous solution A and nitrogen is bubbled for 1-2 h, and then the hydrothermal reaction is carried out at 170-190 ℃ for 3-12 h, after which the cross-scale electrode skeleton is taken out, washed with deionized water and dried, and then annealed at 700 ℃ for 4-6 h to obtain a composite positive electrode.

[0019] Further, in the step 2), the mass ratio of the cross-scale electrode skeleton to the mixed aqueous solution A is 1:10-1:100.

[0020] Further, in the step 3), the Li4Ti5O 12 is in-situ loaded on the cross-scale electrode skeleton by using a hydrothermal reaction, and the process is as follows: a mixed aqueous solution B of lithium hydroxide, hydrogen peroxide and isopropyl titanate is prepared, the concentration of lithium hydroxide is 0.1-0.6 mol / L, the concentration of hydrogen peroxide is 0.1-0.6 mol / L, and the concentration of isopropyl titanate is 0.019-0.113 mol / L; the cross-scale electrode skeleton obtained in the step (1) is immersed in the mixed solution B, and then the hydrothermal reaction is carried out at 120-140 ℃ for 3-12 h, after which the cross-scale electrode skeleton is taken out, washed with deionized water and dried, and then annealed at 550 ℃ for 10-12 h to obtain a composite negative electrode.

[0021] Further, in the step 3), the mass ratio of the cross-scale electrode framework to the mixed aqueous solution B is 1:10-1:100.

[0022] In a preferred embodiment of the present application, the cross-scale electrode framework is a carbon fiber / carbon nanotube cross-scale electrode framework.

[0023] LiFePO4 is loaded on the carbon fiber / carbon nanotube cross-scale electrode framework in situ by a hydrothermal reaction, and the process is as follows: a mixed aqueous solution A of lithium hydroxide, ferrous sulfate and ethylenediaminetetramethylene phosphonic acid is prepared, the concentration of lithium hydroxide is 12 mol / L, the concentration of ferrous sulfate is 4 mol / L, and the concentration of ethylenediaminetetramethylene phosphonic acid is 1 mol / L; the carbon fiber / carbon nanotube cross-scale electrode framework is immersed in the mixed aqueous solution A and nitrogen is bubbled for 1 h, the mass ratio of the carbon fiber / carbon nanotube cross-scale electrode to the mixed aqueous solution A is 1:20, a hydrothermal reaction is carried out at 180℃ for 6 h, after being taken out, the carbon fiber / carbon nanotube cross-scale electrode is washed with deionized water and dried, and then annealing is carried out at 700℃ for 4 h, to obtain a composite positive electrode.

[0024] Li4Ti5O 12 is loaded on the carbon fiber / carbon nanotube cross-scale electrode framework in situ by a hydrothermal reaction, and the process is as follows: a mixed aqueous solution B of lithium hydroxide, hydrogen peroxide and isopropyl titanate is prepared, the concentration of lithium hydroxide is 0.4 mol / L, the concentration of hydrogen peroxide is 0.4 mol / L, and the concentration of isopropyl titanate is 0.075 mol / L; the carbon fiber / carbon nanotube cross-scale electrode framework is immersed in the mixed solution B, the mass ratio of the carbon fiber / carbon nanotube cross-scale electrode to the mixed aqueous solution B is 1:20, a hydrothermal reaction is carried out at 120℃ for 6 h, after being taken out, the carbon fiber / carbon nanotube cross-scale electrode is washed with deionized water and dried, and then annealing is carried out at 550℃ for 10 h, to obtain a composite negative electrode.

[0025] Since the fibrous lithium ion battery is mainly used in the fields of flexible energy storage, wearable energy storage and weavable energy storage, the fibrous lithium ion battery needs to be able to withstand bending deformation, which requires that the composite positive electrode and the composite negative electrode can maintain the stability of the microstructure under deformation conditions. In the present application, by controlling the growth density of the carbon nanotubes, the size and loading amount of LiFePO4 and Li4Ti5O 12 , the size of the LiFePO4 nanospheres and the Li4Ti5O 12 nanosheets is similar to the inter-tube spacing of the carbon nanotubes, so that mechanical support can be provided between the carbon nanotubes to avoid the microstructure of the composite positive electrode and the composite negative electrode from being destroyed under the deformation conditions, and at the same time, the LiFePO4 nanospheres and the Li4Ti5O 12The nanosheet gap forming porous structure can facilitate the infiltration of electrolyte and the transmission of lithium ions, and avoids the decrease of energy storage performance caused by dense electrode structure. The growth density of the carbon nanotubes prepared by the method is 0.1-0.5 mg / cm 2 , the loading amount of LiFePO4 is 1-4 mg / cm 2 , the loading amount of Li4Ti5O 12 is 1-5 mg / cm 2 , the size of LiFePO4 is 10-100 nm, and the size of Li4Ti5O 12 is 50-300 nm. In a preferred embodiment of the present application, the growth density of the carbon nanotubes is 0.34 mg / cm 2 , the loading amount of LiFePO4 is 2.9 mg / cm 2 , the loading amount of Li4Ti5O 12 is 3.2 mg / cm 2 , the size of LiFePO4 is 20-30 nm, and the size of Li4Ti5O 12 is 100-150 nm.

[0026] After the composite positive electrode and the composite negative electrode are fully dried, the composite positive electrode and the composite negative electrode are respectively wrapped with a separator, two electrodes are arranged in a parallel structure in a heat shrinkable tube and lead wires are drawn out, one end of the heat shrinkable tube is sealed by using epoxy resin, electrolyte is injected from the other end of the heat shrinkable tube in an argon-filled glove box, the heat shrinkable tube is shrunk to a proper size by heating, and the opening end of the heat shrinkable tube is sealed by using epoxy resin to complete the assembly of the fiber-shaped lithium ion battery. After the assembled battery is left still overnight, the energy storage performance and the deformation resistance are tested.

[0027] The present application has the following technical effects:

[0028] (1) By growing carbon nanotubes on the fiber-shaped conductive material, a self-supporting current collector with a large specific surface area is formed, the loading amount and utilization rate of active substances are improved, and the linear capacity density and linear energy density of the fiber-shaped lithium ion battery are significantly improved. At the same time, the spacing between the carbon nanotubes provides a channel for the transmission of lithium ions, and the nanoscale LiFePO4 and Li4Ti5O 12 loaded on the carbon nanotubes can also shorten the distance of lithium ion intercalation / deintercalation, thereby improving the rate performance and cycle stability of the fiber-shaped lithium ion battery.

[0029] (2) By controlling the growth density of the carbon nanotubes, the size and loading amount of LiFePO4 and Li4Ti5O 12 , the size and loading amount of LiFePO4 and Li4Ti5O 12The size of the nanosheet is similar to the inter-tube spacing of the carbon nanotube, so that mechanical support can be provided between the carbon nanotubes to avoid the microstructure of the composite positive electrode and the composite negative electrode from being destroyed under deformation conditions, so that the energy storage performance of the fibrous lithium ion battery can be kept stable under bending deformation.

[0030] (3) The linear capacity density of the fibrous lithium ion battery obtained by the application can reach 1.1 mAh / cm, and the linear energy density can reach 2.74 mWh / cm. After the discharge rate is increased from 1C to 10C, the specific capacity retention rate can reach 85%. The discharge specific capacity retention rate under 180° bending conditions reaches 98%, and has good deformation stability, and has wide application prospects in the field of wearable electronics. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The structure of the fibrous lithium ion battery based on the cross-scale electrode skeleton of the application is shown in the figure.

[0032] Figure 2 Scanning electron microscope photos before and after in-situ growth of carbon nanotubes on carbon fibers. Wherein (a) is before in-situ growth, (b) is after in-situ growth.

[0033] Figure 3 Scanning electron microscope photos of loading electrode active material on carbon fiber / carbon nanotube by hydrothermal method. (a) is loading Li4Ti5O 12 nanosheet, (b) is loading LiFePO4 nanosphere.

[0034] Figure 4 Effect of growth of carbon nanotubes on carbon fibers on specific capacity of fibrous lithium ion full battery.

[0035] Figure 5 Specific capacity change of fibrous lithium ion battery based on carbon fiber / carbon nanotube cross-scale electrode skeleton at different discharge rates.

[0036] Figure 6 Charge-discharge curve of fibrous lithium ion battery based on carbon fiber / carbon nanotube cross-scale electrode skeleton under 180° bending and unbending conditions. DETAILED DESCRIPTION

[0037] The following description is exemplary and is intended to provide further explanation of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0038] The chemical reagents and solvents in the present application are commercially available analytical or chemical pure reagents unless otherwise specified. The carbon fiber is T300 type from Toray Industries, Inc. of Japan; the carbon nanotube fiber is purchased from Beijing Deke Daojin Technology Co., Ltd., with a diameter of 1-5 μm; the graphene fiber is purchased from Suzhou Yanxinshuoshen New Material Technology Co., Ltd., with a model number of 75D / 48F; the nickel wire and the stainless steel wire are commercially available, with a diameter less than 500 μm; the separator is a commercially available Celgard 2500 polypropylene separator; the electrolyte is a commercially available LiPF6 lithium ion battery electrolyte, with 1 mol / L LiPF6 as a solute, and ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1 as solvents; and the heat shrink tube is a commercially available polyethylene heat shrink tube.

[0039] The present application is further described below in conjunction with examples.

[0040] Example 1

[0041] A bundle of 10 carbon fibers is used as a fibrous conductive material, and carbon nanotubes are grown in situ on the carbon fiber bundle by chemical vapor deposition. A carbon source solution containing a catalyst is prepared, which is a mixed solution of ethanol, dimethylbenzene, ethylenediamine and ferrocene, with ferrocene as the catalyst, wherein the volume ratio of ethanol, dimethylbenzene and ethylenediamine is 1:1:0.1, and the concentration of ferrocene is 0.2 mol / L. The surface of the carbon fiber bundle is cleaned with deionized water and ethanol, and after drying, the carbon fiber bundle is placed in a high-temperature tube furnace, argon is introduced, and the temperature is raised to 850°C. Then, the carbon source solution containing the catalyst is injected into the tube furnace for carbon nanotube growth, with an injection speed of 2 mL / h and a growth time of 10 min. A carbon fiber / carbon nanotube cross-scale electrode skeleton is obtained.

[0042] LiFePO4 is loaded in situ on the carbon fiber / carbon nanotube cross-scale electrode skeleton by hydrothermal reaction. A mixed aqueous solution A of lithium hydroxide, ferrous sulfate and ethylenediaminetetramethylenephosphonic acid is prepared, with a lithium hydroxide concentration of 12 mol / L, a ferrous sulfate concentration of 4 mol / L, and an ethylenediaminetetramethylenephosphonic acid concentration of 1 mol / L. The carbon fiber / carbon nanotube cross-scale electrode skeleton is immersed in the mixed aqueous solution A and nitrogen is bubbled for 1 h, with a mass ratio of the carbon fiber / carbon nanotube cross-scale electrode to the mixed aqueous solution A of 1:20. Hydrothermal reaction is carried out at 180°C for 6 h, and after being taken out, the product is washed with deionized water and dried. Subsequently, annealing is carried out at 700°C for 4 h, and a composite positive electrode is obtained.

[0043] Li4Ti5O 12A mixed aqueous solution B of lithium hydroxide, hydrogen peroxide, and isopropyl titanate was prepared, with the concentrations of lithium hydroxide (0.4 mol / L), hydrogen peroxide (0.4 mol / L), and isopropyl titanate (0.075 mol / L). A carbon fiber / carbon nanotube multiscale electrode framework was immersed in the mixed solution B, with a mass ratio of 1:20 between the carbon fiber / carbon nanotube multiscale electrode and the mixed aqueous solution B. The mixture was subjected to a hydrothermal reaction at 120℃ for 6 hours. After removal, it was washed with deionized water and dried, followed by annealing at 550℃ for 10 hours to obtain a composite negative electrode.

[0044] After thoroughly drying the composite positive and negative electrodes, they were separately wrapped with separators. The two electrodes were then installed in parallel within heat-shrink tubing with lead wires extending out. One end of the heat-shrink tubing was sealed with epoxy resin. Electrolyte was injected into the other end of the heat-shrink tubing in an argon-filled glove box. The heat-shrink tubing was heated to shrink to the appropriate size, and the open end of the heat-shrink tubing was sealed with epoxy resin to complete the assembly of the fibrous lithium-ion battery. After the assembled battery was left to stand overnight, its energy storage performance and deformation resistance were tested.

[0045] The carbon fiber / carbon nanotube multiscale electrode framework prepared in this embodiment has a uniform microstructure, such as... Figure 2 As shown, arrayed carbon nanotubes can be grown in situ on carbon fibers, with a growth density of 0.34 mg / cm³. 2 After hydrothermal reaction, nanosheet-like Li4Ti5O can be in situ loaded onto carbon fibers / carbon nanotubes. 12 ( Figure 3 a) and nanosphere-shaped LiFePO4 ( Figure 3 b), Li4Ti5O 12 The size is 100–150 nm, and the loading is 3.2 mg / cm³. 2 The size of LiFePO4 is 20–30 nm, and the loading is 2.9 mg / cm³. 2 .

[0046] The assembled fibrous lithium-ion battery exhibits excellent energy storage performance, with a specific capacity of up to 145 mAh / g, while the specific capacity of the fibrous lithium-ion battery based on carbon fiber bundles without carbon nanotube growth is only 130 mAh / g. Figure 4 Calculations show that the linear capacity density of the fibrous lithium-ion battery based on the carbon fiber / carbon nanotube multi-scale electrode framework can reach 1.1 mAh / cm², and the linear energy density can reach 2.74 mWh / cm². After increasing the discharge rate from 1C to 10C, the specific capacity retention rate can reach 85%, demonstrating excellent rate performance. Figure 5 The discharge specific capacity retention rate reached 98% under 180° bending conditions. Figure 6), which has good deformation stability and wide application prospects in the field of wearable electronics.

Claims

1. A method for the preparation of a fibrous lithium-ion battery based on a cross- scale electrode skeleton, characterized in that, The method comprises the following steps: 1) growing carbon nanotubes on the surface of the fibrous conductive material as a cross-scale electrode skeleton by a chemical vapor deposition process; 2) loading LiFePO4 on the cross-scale electrode skeleton in situ as a composite positive electrode by a hydrothermal reaction; 3) In-situ loading of Li4Ti5O12 on cross-scale electrode scaffolds using hydrothermal reaction 12 as a composite anode; 4) wrapping the composite positive electrode and the composite negative electrode with a separator respectively, loading into a heat shrinkable tube, filling with electrolyte, and packaging to obtain the fibrous lithium ion battery; In step 1), the fibrous conductive material is selected from any one of carbon fiber, carbon nanotube fiber, graphene fiber, nickel wire and stainless steel wire; In step 1), the chemical vapor deposition process is as follows: washing the surface of the fibrous conductive material with deionized water and ethanol, drying, placing the fibrous conductive material in a high-temperature tube furnace, passing in argon and heating to 850℃, then injecting a carbon source solution containing a catalyst into the tube furnace for carbon nanotube growth, the injection speed is 2-20 mL / h, and the growth time is 5-30 min; In step 2), the hydrothermal reaction is used to load LiFePO4 on the cross-scale electrode skeleton in situ, and the process is as follows: preparing a mixed aqueous solution A of lithium hydroxide, ferrous sulfate and ethylenediaminetetramethylene phosphonic acid, the concentration of lithium hydroxide is 6-36 mol / L, the concentration of ferrous sulfate is 2-12 mol / L, and the concentration of ethylenediaminetetramethylene phosphonic acid is 0.5-3 mol / L; immersing the cross-scale electrode skeleton obtained in step (1) into the mixed aqueous solution A and passing in nitrogen for 1-2 h, hydrothermal reaction at 170-190℃ for 3-12 h, washing with deionized water after taking out and drying, then annealing at 700℃ for 4-6 h to obtain the composite positive electrode; In the step 3), the Li4Ti5O12 is loaded on the cross-scale electrode framework in situ by using a hydrothermal reaction 12 The process is as follows: a mixed aqueous solution B of lithium hydroxide, hydrogen peroxide and isopropyl titanate is prepared, the concentration of lithium hydroxide is 0.1-0.6 mol / L, the concentration of hydrogen peroxide is 0.1-0.6 mol / L, and the concentration of isopropyl titanate is 0.019-0.113 mol / L; the cross-scale electrode framework obtained in the step (1) is immersed in the mixed solution B, and a hydrothermal reaction is carried out at 120-140 ℃ for 3-12 h; after being taken out, the cross-scale electrode framework is cleaned with deionized water and dried, and then annealed at 550 ℃ for 10-12 h to obtain the composite negative electrode.

2. The production method according to claim 1, characterized by, In step 1), the diameter of the fibrous conductive material is 1-500 μm.

3. The preparation method according to claim 1, characterized in that, In step 1), the carbon source solution containing a catalyst is a mixed solution of ethanol, dimethylbenzene, ethylenediamine and ferrocene, and ferrocene is used as a catalyst, wherein the volume ratio of ethanol, dimethylbenzene and ethylenediamine is 1:1:0.1-0.2, and the concentration of ferrocene is 0.1-0.2 mol / L.

4. The method of claim 1, wherein, In step 2), the mass ratio of the cross-scale electrode skeleton to the mixed aqueous solution A is 1:10-1:

100.

5. The preparation method according to claim 1, characterized in that, In step 3), the mass ratio of the cross-scale electrode skeleton to the mixed aqueous solution B is 1:10-1:100.

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